92 



THE PALEONTOLOGY OF MINNESOTA. 



IStreptulasma. 



STKEPTELASMA BREVE n. sp. (Ulrich). 



FIG. 7. 



Fig. 7, Streptelasma breve Ulrich, Galena limestone, near Fountain, Minnesota, a, an average speci- 

 men, natural size ; b, an unusually straight example ; c, the flattened but entire calyx of 

 another specimen ; d, represents the greater part of the calyx of a fourth example, x 2, showing 

 the central union and arrangement of the septa and foveaa in u very clear manner. 



Corallum free, simple, conical, small, curved, expanding very rapidly, the width 

 greater than the hight. An average specimen is about 1 1 mm. high and 16 mm. wide 

 across the cup. In a small specimen the measurements are, respectively, 7 and 

 11 mm. Surface marked with fine encircling lines and stronger annulations of 

 growth ; occasionally also with delicate vertical ribs. The latter seem, however, to 

 be restricted to the lower half of the corallum. Calyx deeply concave, the bottom 

 extending to a point a little beneath the middle of the hight. Septa large and 

 small, the latter shown only in the extreme outer part of complete calices, the 

 ortner extending to the center where they unite into four bundles of from six to 

 eight in each. Principal septum straight, sometimes stronger than the others, 

 extending to the center through a well marked fovea. The septa on each side of it 

 arranged in a pinnate manner, uniting centrally. Lateral foveae narrow, but gen- 

 erally recognizable. Opposite septum forming the central one of usually fifteen 

 septa that are radially arranged in the half of the calyx on the shorter or concave 

 side of the corallum. As a rule it is distinguished by its greater strength and prom- 

 inence. Lateral septa inconspicuous, shorter than the others. Total number of 

 septa in a specimen of the average size about sixty-four, of which thirty-two are 

 large and long, while an equal number belong to the intermediate rudimentary set. 

 All of them seem to have been obscurely dentate, and but little elevated, so that 

 they are to be termed ridge-shaped rather than lamellate. At the center of the 

 calyx the septa inosculate, forming a limited number of cells bounded by spinulose 

 walls. As shown in fig. 2d, the condition described is scarcely to be called a twist- 

 ing of the septa. Internal structure unknown. 



